Field-Aligned Currents and Large-Scale Ionospheric Disturbances - A New Basis for Understanding Prompt Penetration Electric Field (PPEF)

Prompt Penetration Electric Field (PPEF) is known to occur when solar wind IMF orientation changes abruptly which causes a fraction of the high-latitude electric fields to penetrate spontaneously to the middle- and low-latitude ionosphere (Tsurutani et al., 2008). Waghule and Knipp (2023) investigated some extreme geomagnetic storms which compressed the magnetopause to within the geosynchronous orbit, and identified that during such extreme forcing conditions, large-scale Region-1 (R1) Field Aligned Currents (FAC) appear to extend to lower latitudes. Lu et al. (2020) have done a detailed model-data comparative study of ionospheric disturbances such as traveling ionospheric disturbances (TIDs) and storm-enhanced density (SED) of the March 17, 2015 St. Patrick's Day storm - which is one of the storms under our investigation. The authors identified a PPEF signature in their investigation of understanding TID signatures using TEC data across different latitudes over the span of the storm.

Upon exploring the patterns in the latitudinal and longitudinal Total Electron Content (TEC) perturbation maps at subauroral latitude for high solar wind compression storm events, we have found some temporal correlation between Region 1 FAC extension to lower latitudes and signatures of PPEFs. These appear to be sudden global ionospheric disturbances (SGID).

FAC patterns are derived from Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) data using Optimal Interpolation (OI) method and are presented in the forms of individual polar plots and as keograms, which show temporal variations of FACs spatial patterns over 24 hours (Shi et al., 2020). The TEC perturbation maps for spatial variations were created using GNSS data obtained by detrending TEC with a 30-min running mean- for all links between a ground-based GNSS receiver and visible navigation satellites. (Lu et al., 2020)

We note that the PPEF signatures appear in both latitude and longitude TEC perturbation keograms, some at the same time (implying global PPEF) and some at different times (local PPEF). These signatures seem to coincide with the FAC R1 extensions. Since PPEFs move through a range of latitudes it makes sense that R1 extension has some correlation with PPEF signatures. To understand this correlation, we analyze solar wind parameters - particularly Interplanetary Magnetic Field (IMF) Bz - along with derived parameters of flow pressure, Auroral Electrojet index (AE), and Asym-H index were also analyzed using OMNIwebdata.

Tsurutani et al. (2008) consider a number of factors influencing PPEF during the great magnetic storm of 30–31 October 2003 which are relevant in the events under investigation. We find that PPEFs are not always due to IMF Bz turning southward but can be associated with substorms (Fejer & Navarro, 2022) and compression (Nilam et al., 2020). This observation could be a new basis for understanding PPEFs, but further investigation needs to be done.